NAME

SYNTAX

void caldate_frommjd(&cd,day,weekday,yearday);
long caldate_mjd(&cd);
void caldate_normalize(&cd);

void caldate_easter(&cd);

struct caldate cd;
long day;
int *weekday;
int *yearday;

BASIC CONVERSIONS

caldate_frommjd puts into cd the date corresponding to the modified Julian day number day.

caldate_frommjd also computes the day of the week (0 through 6) and the day of the year (0 through 365). It stores the day of the week in *weekday if weekday is nonzero. It stores the day of the year in *yearday if yearday is nonzero.

caldate_mjd returns the modified Julian day number corresponding to the date in cd.

caldate_mjd accepts days outside the range 1 to 31, referring to days before the beginning or after the end of the month. It also accepts months outside the range 1 to 12, referring to months before the beginning or after the end of the year.

caldate_normalize calls caldate_frommjd with the result of caldate_mjd. This means that it accepts out-of-range months and out-of-range days in cd, and puts a valid calendar date back into cd.

OTHER FUNCTIONS

LIMITATIONS

The Gregorian calendar will be replaced by a new calendar within a few thousand years. The caldate_frommjd and caldate_mjd routines will be upgraded accordingly. The current caldate_frommjd and caldate_mjd routines are not useful for dates far in the future.

Day numbers will overflow a 32-bit long sometime after the year 5000000; all systems should upgrade to 64-bit longs before then. caldate_mjd does not check for overflow.

SEE ALSO